Various non-invasive methods for measuring glucose in body tissue have been known. In particular, U.S. Pat. No. 5,792,668 by Fuller et al. describes a device where a square wave signal or a plurality of sine waves with differing frequencies are fed to a first electrode applied to the tissue. A second electrode is used for measuring a signal transmitted through the tissue. The phase and/or amplitude of the transmitted signal are used for determining the glucose level.